Adaptive load blinder for distance protection Hassan Khorashadi Zadeh a,⇑ , Zuyi Li b a Siemens Energy Inc. Transmission Division, 7000 Siemens Road, Wendell, NC 27591, United States b Illinois Institute of Technology, Department of Electrical and Computer Engineering, 3301S. Dearborn Street, Chicago, IL 60616, United States a r t i c l e i n f o Article history: Received 2 August 2009 Received in revised form 26 September 2010 Accepted 22 November 2010 Keywords: Distance relay Load blinder Load encroachment Loadability Blackout Artificial neural network a b s t r a c t This paper proposes a novel adaptive load blinder for distance protection. A distance relay can provide remote backup protec tion by zone s 2 and 3, but it may mal-op erat e unde r hea vy load ing conditio ns and cause cascading trips in the network, which could further lead to a widespread blackout. To prevent cascading outages, load blinders or load encroachment elements are generally used to block the distance relay when there is heavy load in the system. However, these elements are not always able to discrim- inate heavy loading conditions from fault conditions, especially for heavy loads with low power factors or faults with fault resistance. This paper presents a novel load blinder scheme for distance protection by using artificial neural network (ANN). Test results show that the proposed ANN-based load blinder sche me is able to discr imin ate between diffe rent heav y load s with a wide rang e of power factor s and dif- ferent faults with fault resistance. 2011 Elsevier Ltd. All rights reserved. 1. Introduction Tra nsmissio n line protec tion is the most elab ora te and chal- lenging function in power system protection. About two thirds offaults in power systems occur on the transmission line network. Conseque ntl y, it has re cei ved extensive att ent io n fro m the researchers and designers in the area of power system protection. Distance protection is the most common transmission line pro- tection. Zone 1 of a distance relay is used to provide primary high- spe ed pro tecti on of a sign ificant por tion of a tran smi ssion line. Zone 2 is used to cover the rest of the protected line and provide some backup for the remote end bus. Zone 3 is the backup protec- tion for all the lines connected to the remote end. The impedance of loads can be actually less than the impedance of some faults in very long and heav ily load ed tran smi ssio n line app lica tions . This phenomenon may cause distance relays to mal-operate. Studies of several large blackouts during the past decades indi- cate that backup zones of distance relays are involved in most ofthe major blackout incidences, such as the Northeast Blackout on Nov emb er 9, 1965[2] , the New Yor k Cit y Bla cko ut on Jul y 13, 1977 [3] , the West Coast Blackout on July 2, 1996 [4] , the West Coast Blackout on August 10, 1996[4], and the Northeast Blackout on August 14, 2003[5]. Many of the operations of zone 3 of distance relays, during ma- jor disturbances, wer e caus ed by line ove rloa ding cond itio ns [1] . The undesired operation of zone 3 distance relays caused by line ove rloa ds is the most obvious distance relay char acter istic s that have been widely discuss ed afte r the Aug ust 14, 2003 blacko ut [6–8]. Beca use zone 3 dista nce relay operati ons (or other over- rea ching zone ope rati ons) have cont ributed to the seve rity ofbla cko uts, a lot of eff or ts hav e bee n pl ace d into reviewi ng the ir set - tings and developing loadability requirements and standards. The protection relays must be made selective enough to discriminate between load and fault conditions. Difference between loads and unsy mmetrical faults can be dete cted by unba lanc e cond ition s. However, it is more difficult to discriminate between heavy loads and thr ee -phas e faults. One sol uti on is to use len tic ula r or ell iptical shape characteristics for load rejection. Unfortunately, these char- acteristics reduce the fault-resistance coverage[9]. Another solu- tion is to use additional comparators to make blinders parallel to the tran smi ssion line char acte rist ics. However , it wil l limit the impedance pla ne coverage thus exclude load from the trip ping characteristics [10]. All traditional solutio ns are based on the same idea: to shape the operating characteristics of the relay to avoid or minimize load encroachment. The traditional solutions have some disadvantages: Reducing the size of the relay characteristics desensitizes the relay to faults with resistance[11]. Notice that some symmetri- cal faults as shown in Fig. 1with fault resistance can affect the impedance measured by distance relay. Avoiding a small area of load encroachment often requires the sacrifice of much larger areas of fault coverage [11]. 0142-0615/$ - see front matter2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.ijepes.2010.11.012 ⇑ Corresponding author. Tel.: +1 3125196976. E-mail address: [email protected](H. Khorashadi Zadeh). Electrical Power and Energy Systems 33 (2011) 861–867 Contents lists available at ScienceDirect Electrical Power and Energy Systems journal homepage: www.elsevier.com/locate/ijepes
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8/9/2019 Adaptive load blinder for distance protection.pdf
a Siemens Energy Inc. Transmission Division, 7000 Siemens Road, Wendell, NC 27591, United Statesb Illinois Institute of Technology, Department of Electrical and Computer Engineering, 3301S. Dearborn Street, Chicago, IL 60616, United States
a r t i c l e i n f o
Article history:
Received 2 August 2009
Received in revised form 26 September
2010
Accepted 22 November 2010
Keywords:
Distance relay
Load blinder
Load encroachment
Loadability
Blackout
Artificial neural network
a b s t r a c t
This paper proposes a novel adaptive load blinder for distance protection. A distance relay can provide
remote backup protection by zones 2 and 3, but it may mal-operate under heavy loading conditionsand cause cascading trips in the network, which could further lead to a widespread blackout. To prevent
cascading outages, load blinders or load encroachment elements are generally used to block the distance
relay when there is heavy load in the system. However, these elements are not always able to discrim-
inate heavy loading conditions from fault conditions, especially for heavy loads with low power factors
or faults with fault resistance. This paper presents a novel load blinder scheme for distance protection
by using artificial neural network (ANN). Test results show that the proposed ANN-based load blinder
scheme is able to discriminate between different heavy loads with a wide range of power factors and dif-
ferent faults with fault resistance.
2011 Elsevier Ltd. All rights reserved.
1. Introduction
Transmission line protection is the most elaborate and chal-
lenging function in power system protection. About two thirds of
faults in power systems occur on the transmission line network.
Consequently, it has received extensive attention from the
researchers and designers in the area of power system protection.
Distance protection is the most common transmission line pro-
tection. Zone 1 of a distance relay is used to provide primary high-
speed protection of a significant portion of a transmission line.
Zone 2 is used to cover the rest of the protected line and provide
some backup for the remote end bus. Zone 3 is the backup protec-
tion for all the lines connected to the remote end. The impedance
of loads can be actually less than the impedance of some faults
in very long and heavily loaded transmission line applications. This
phenomenon may cause distance relays to mal-operate.Studies of several large blackouts during the past decades indi-
cate that backup zones of distance relays are involved in most of
the major blackout incidences, such as the Northeast Blackout on
November 9, 1965 [2], the New York City Blackout on July 13,
1977 [3], the West Coast Blackout on July 2, 1996 [4], the West
Coast Blackout on August 10, 1996 [4], and the Northeast Blackout
on August 14, 2003 [5].
Many of the operations of zone 3 of distance relays, during ma-
jor disturbances, were caused by line overloading conditions [1].
The undesired operation of zone 3 distance relays caused by line
overloads is the most obvious distance relay characteristics that
have been widely discussed after the August 14, 2003 blackout
[6–8]. Because zone 3 distance relay operations (or other over-
reaching zone operations) have contributed to the severity of
blackouts, a lot of efforts have been placed into reviewing their set-
tings and developing loadability requirements and standards. The
protection relays must be made selective enough to discriminate
between load and fault conditions. Difference between loads and
unsymmetrical faults can be detected by unbalance conditions.
However, it is more difficult to discriminate between heavy loads
and three-phase faults. One solution is to use lenticular or elliptical
shape characteristics for load rejection. Unfortunately, these char-
acteristics reduce the fault-resistance coverage [9]. Another solu-
tion is to use additional comparators to make blinders parallel to
the transmission line characteristics. However, it will limit theimpedance plane coverage thus exclude load from the tripping
characteristics [10]. All traditional solutions are based on the same
idea: to shape the operating characteristics of the relay to avoid or
minimize load encroachment. The traditional solutions have some
disadvantages:
Reducing the size of the relay characteristics desensitizes the
relay to faults with resistance [11]. Notice that some symmetri-
cal faults as shown in Fig. 1 with fault resistance can affect the
impedance measured by distance relay.
Avoiding a small area of load encroachment often requires the
sacrifice of much larger areas of fault coverage [11].
0142-0615/$ - see front matter 2011 Elsevier Ltd. All rights reserved.doi:10.1016/j.ijepes.2010.11.012